The invention relates to a process of coating a metallic surface with a composition for coating with a pretreatment composition prior to organic coating, with a passivation composition without intent for subsequent organic coating, with a pretreatmentprimer composition or with a primer composition, with a paint composition or with an electrocoating composition wherein each one composition contains nanoparticles on the base of at least one layered double hydroxide (LDH) phase showing the general formula [1],[M2+(1±0.5)−x(M3+,M4+)x(OH)2±0.75]An−x/n.mH2O  [1],wherein M2+, M3+ and M4+ are divalent, trivalent resp. tetravalent cations, or calcined or calcined and rehydrated particles of this LDH phase. The invention further relates to a method of use of nanoparticles on the base of LDH in aqueous and non-aqueous coating compositions and to the thereof generated coatings.
The processes most commonly employed in surface treatment for metallic surfaces are the treatment of metallic surfaces without intent of subsequent organic coating, often called passivation, especially of parts, coil or coil portions like sheets made of at least one metallic material, and the pretreatment of metallic surfaces prior to organic coating like lacquering or application of adhesives. Such treatments and pretreatments are frequently based on the one hand on the use of chromium(VI) compounds, optionally together with diverse additives, or on the other hand on the base of phosphates like zinc/manganese/nickel phosphates, on the base of Ti and/or Zr containing compounds, on the base of silane/silanol/siloxane and/or on the base of organic polymers/copolymers together with diverse additives.
Primer and paint compositions are typically based on aqueous or non-aqueous compositions with a high content of organic polymer/copolymer. A primer is the first organic coating especially after pretreatment coating with a conversion coating of the first or second type. They are developed in very many chemical variations and used very much.
Pretreatmentprimer compositions are typically based on aqueous or non-aqueous compositions with a high content of organic polymer/copolymer too. A pretreatmentprimer is the first organic coating on a metallic surface, which combines and fulfils the tasks and properties of a pretreatment or passivation composition resp. coating with the tasks and properties of a primer composition respectively primer coating.
Electrocoating (=electrodeposition coating, e-coat, e.g. cathodic) compositions for electrocoating a pretreated metallic surface with an aqueous electroconductive primer composition is in many cases the primer in car-body production. Often, the electrocoating will be a cathodic electrocoating. Such electrocoating compositions contain a small amount of electroconductive substance especially like on the base of copper, indium, lead, tin and/or yttrium. Because of the toxicological and ecological risks associated especially with processes using chromate or nickel, alternatives to these processes in all the areas of surface technology for metallic substrates have been sought for many years, but it has repeatedly been found that, in many applications, completely chromate-free or nickel-free processes do not satisfy 100% of the performance spectrum or do not offer the desired safety, especially in the construction of aircrafts. Attempts are therefore being made to minimize the chromate contents or nickel contents and to replace Cr6+ with Cr3+ as far as possible. High-quality phosphatizing processes are used especially in the automobile industry, e.g. for the pretreatment of car bodies prior to lacquering, which have maintained the quality of automobile corrosion protection at a high level. Zinc-manganese-nickel phosphatizing processes are conventionally employed for this purpose. In the last years, more and more aqueous compositions on the base of Ti and/or Zr containing compounds, on the base of silane/silanol/siloxane and/or on the base of organic polymers/copolymers have been developed and partially successfully used.
The term “paint” shall mean in the sense of the present invention any paint, any lacquer or any paint-like composition especially adapted to a specific use to coat metallic surfaces which may be used for example as primer, as base coat, as topcoat, as clear coat and/or for coil-coating, but it does not cover pretreatmentprimer, primer and electrocoating compositions. It covers in the same way high solids' paints, water based systems, solvent based systems and primers. The term “pretreatmentprimer” does not cover pretreatment and primer compositions.
For the use in primer and paint compositions, many corrosion inhibiting compounds and mixtures are offered, but many of these are not or not for the amount the corrosion inhibitor should be added sufficiently compatible with the primer or paint composition. If there is an inadequate corrosion inhibitor added to a primer or paint composition or if it is added in an amount that is not compatible with the primer or paint composition, the protected metallic surface may even corrode easier because of this corrosion inhibitor due e.g. blistering effects, lack of barrier properties or loss of adhesion.
The use of silane/silanol/siloxane, water glass or organic polymer/copolymer in aqueous compositions for the production of anticorrosive coatings is known in principle. These coatings are not always formed with outstanding properties. The corrosion protection and the lacquer adhesion of such coatings formed are often high, but not always. But there exist several applications on metallic surfaces, where the requirements for corrosion resistance and/or lacquer adhesion are very high and not yet fulfilled.
It is known from EP 1 088 853 B1 to use Mg—Al-based hydrotalcite-type particles, which may be coated with higher fatty acid, organosilane compound or rosin, as a stabilizer in chlorine-containing resins. Without such stabilizer, these chlorine-containing resins are susceptible to heat deterioration and oxidation degradation.
U.S. Pat. No. 5,266,356 discloses a method for forming lithium rich films which are particle-free LDH based conversion coating films on the surface of Al—Li alloys. In the bath solution, Li+ enters aluminium hydroxide to form a LDH-based phase.